This invention relates to a hydraulic snubber for a grapple and, more particularly, to a snubber including a hydraulic fluid supply system for an internally provided piston which assists in the snubbing action between the snubber housing and the associated clevises.
This invention is an improvement on co-owned U.S. Pat. No. 4,810,020 and reference may be had thereto for details of construction and operation not specifically set forth herein. Generally, the grapple of the '020 patent has been employed in the skidding of logs and required freedom of movement in two mutually perpendicular planes. However, when the grapple was free, it required snubbing against free pivotal movement; otherwise, it could cause injury to logging personnel and damage to the grapple itself by crashing into the boom.
The '020 patent provided an internal ring piston for the hydraulic snubber and employed a special grease inlet fitting to protect against excessive external pressure so as to minimize the chance of undesired leakage and also to restrict the degree of snubbing. However, this required a special adapter assembly to prevent use of a grease gun with a standard ("automotive") type nozzle. While the adapter assembly worked well, there have been customer complaints about using it--to the extent that some customers refused to use it. That meant that there was no overload protection for the springs--resulting in flattening of the springs and loss of the object of the snubber. According to the invention, this disadvantage has been overcome. More specifically, the need for a special adapter assembly has been avoided--and without sacrificing overload protection.
According to the invention, the single check valve fitting which was incorporated into the snubber housing passage communicating with the annular piston groove has been replaced by a pair of spaced apart check valves defining a chamber therebetween. The outer check valve allows hydraulic fluid to be introduced through a standard automotive type grease gun. Connecting the chamber with the housing exterior is a pressure relief passage equipped with a pressure relief valve.